JPH0264008A - Single crystal of lanthanide silicate useful as scintillator for detecting x-rays and/or gamma rays - Google Patents

Abstract

PURPOSE: To produce a monocrystal of silicate of a rare earth element usable as a scintillator having a specified composition formula and capable of obtaining an improved performance in comparison with the monocrystal obtained by using well-known oxyolketosilicate.

CONSTITUTION: This scintillator is composed of the monocrystal of silicate of lanthanide expressed by formula I. In formula I, Ln and Ln' are different from each other and represent a rare earth element selected among La, Gd, Yb and Lu and x₁, x₂ and x₃ are such that 0≤x₁<1, 0≤x₂≤0.05, 0≤x₃≤0.05, 0<x₂+x₃≤0.1, 0<x₁+x₂+x₃<1. A detector of X-ray and/or γ-ray is constituted by incorporating the scintillator and a photoelectric detector for detecting light radiated from the scintillator.

COPYRIGHT: (C)1990,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to single crystals of lanthanide silicates useful as scintillators for the detection of X-rays or gamma rays. More particularly, the present invention relates to medical imaging or non-destructive testing of objects such as nuclear waste containers, as well as positron emission tomography related to oil exploration.
The present invention relates to the production of scintillators with application for scintillation tomography.

A scintillator is a substance that makes it possible to convert X-rays and l or gamma rays into low-energy photon radiation, especially in the passband of a photomultiplier tube.
S band).

Among the materials useful as scintillators are mixed oxides of silicon, particularly those with the formula as described in U.S. Pat. No. 4,647,781: and X and y
Rare earth oxyorthosilicates have been recently developed, denoted by y (with values such as 0,1).

The performance of the above-mentioned materials can be evaluated based on the following parameters d: material density 2: effective atomic number ■=scintillation luminous intensity ■: luminescence decay rate.

These parameters create a figure of performance.
ofmerit), F=dZ5I/v can be defined.

In this performance factor F, the numerical value dZ5 characterizes the absorption coefficient of X-rays and l or gamma rays, and the factor I/
v represents the characteristics of the luminescent ion and the crystal environment of the ion.

Scintillators formed from these rare earth oxyorthosilicates give particularly satisfactory results for applications in positron emission tomography. However, the performance characteristics of these scintillators could be further improved, in particular with faster luminescence decay and higher emitters.
ssion 1ntensity).

The present invention particularly relates to new single crystals of rare earth silicates useful as scintillators which provide improved performance compared to those obtained using known oxyorthosilicates.

According to the present invention, a single crystal of a lanthanide silicate useful as a scintillator for the detection of X-rays and l or gamma rays has the formula: %formula%, where Ln and Ln' are Different from each other, La, Gd,
represents a rare earth element selected from Yb and Lu,
And Xl, X2 and X3 are characterized by being equal to 0 < Xi < 1 0 (X2 (0,05 0(X3 (0,05 0 < x2 + x3 < 0.1 0 < X1 + X2 + .

According to a first embodiment of the invention, Xl and X3 are equal to O. In this case, the lanthanide silicate has the formula: %formula %, where X2 corresponds to 0<X2 (0-05, preferably 0.005, with x2<, 0.02).

For example, x2 can vary between 0.01 and 0.011 and corresponds to a silicate with the formula: %.

These silicates have an emission wavelength of approximately 410 nm at ambient temperature.
has.

According to a second embodiment of the invention, X1=0. In this case, the lanthanide silicate has the formula: %formula %) (wherein Ln represents a rare earth element selected from La, Gd, Yb and Lu, and X2 and X3 have the formula: %formula%) < X3 (0,05 preferably 0.003 (X2 (0,01 0,005) corresponds to

Examples of rare earth silicates with this formula include silicates with X2 of 0.005 and 0.0.
Mention may be made of rare earth silicates whose X3 varies between 0.016 and 0.017.

Such rare earth silicates have high emission wavelengths ranging from 500 to 550 nm due to the coexistence of cerium and terbium.

According to a third embodiment of the invention, X3=0. In this case, the rank nido silicate has the formula: % formula %) (wherein Ln and Ln' are different from each other, La, Gd,
represents a rare earth element selected from Yb and Lu, and xl and x2 are 0<xl<1 0<X2<0.05 0<X1+x2<1, preferably 0.05(Xl(0 , 2 0,005 < x2 0.02 0.055 < XI + X2 < 0.22).

For example, X□ can vary between 0°1 and 0.11, and X2 can vary between 0.01 and 0.011. This type of silicate is represented by the formula: %Formula %).

According to a fourth embodiment of the invention, Xl, x2 and X3 are all greater than O. In this case, X engineering, x2
and X3 is 0 < Xl < 1 0 < X2 (0,05 0 < Xa (0,05 preferably 0.05 (xl <, 0.2 0.003 ( ,02.

For example, xo is between 0.1 and 0.11, X2 is 0.0
between 5 and 0.06, and X3 is between 0.01 and 0.0
11.

Silicates of this type have the formula: %Formula %) These silicates also emit light in the wavelength range between 500 and 550 nm due to the coexistence of cerium and terbium.

The rare earth silicates activated with cerium and optionally terbium used in the present invention are known compounds and are published in the Journal of the Electrochemical Society (J, Electrochem).

Soc, ) published by J, J, Lammers (L
ammers) and G, Brasse
Author: Solid-State Science and Technology (Solid-8tate 5science)
and Technology), 1987, 206
As described in the paper on pages 8 to 2071, it has a phosphatite-type structure. In this paper, the silicates are prepared in the form of powders and their luminescence is determined while being excited by ultraviolet or X-ray radiation. Oxyorthosilicate Gd2510s activated by terbium
was also studied, and the conclusion of the paper was that Ce3+ and Tb
The silicates according to the invention activated by 3+ are relatively ineffective as fluorophores, whereas the Gd2S
Oxyorthosilicates such as iO5 have been shown to be superior.

It thus appears from the above article that these single crystals of these same silicates are better scintillators than the oxyorthosilicates described in the above article and in U.S. Pat. No. 4,647,781. It was not possible to infer that it had any performance.

The single crystals of lanthanide silicates according to the invention are produced from lanthanide silicate powders obtained by conventional methods, such as for example by mixing the corresponding oxides Ln2O3, Ln'203, CeO2 or Ce2O3, Tb2O3 and 5tO2. can do. After mixing the powder, heat treatment is performed. This heat treatment makes it possible to obtain the lanthanide silicate according to the present invention. The temperatures employed are generally above 1000° C. and are chosen as a function of the nature of the constituent oxides and their proportions.

Also, Ln3+Ln+ in an aqueous or non-aqueous solvent
Lanthanide silicate powders can also be prepared by precipitation from soluble compounds of 3+, 3i4+, Ce" (n = 3 or 4), and Tb3+. The salt used can be, for example, acetate, and the precipitation can be obtained by adding ammonia.The powder can then be prepared using conventional single crystal production methods, in particular Czochralski (Cz
ochralski) method to convert it into a single crystal.

For this purpose, the powder is placed in a crucible, heated to the melting temperature of the silicate or to the melting temperature protected from atmospheric oxygen so as to form a molten bath, and then the crystal orientation of the hexagonal lattice of the silicate is A single crystal can be produced from the melt bath by the Czochralski method using a single crystal volume of the composition cut parallel to C or crystal direction a. This single crystal volume is brought into contact with the bath and then gradually pulled up with a rotational movement relative to the core itself, ensuring progressive growth of single crystals at the ends of the core in the direction indicated by the core. This method can produce large single crystals suitable for scintillator industry.

Cut a parallelepiped in the single crystal, then polish the two end faces, and then attach the parallelepiped to count the number of X photons and l or gamma photons that are intercepted by one face of the parallelepiped. It can be combined with a photomultiplier tube.

The invention thus also relates to an X-ray and l- or gamma-ray detector comprising a scintillator consisting of a lanthanide silicate single crystal according to the invention and a photoelectric detector for detecting the light from the scintillator. .

In the lanthanide silicate single crystal according to the present invention,
Depending on the amount of cerium and possibly terbium added as dopants, the properties of the scintillator, in particular its luminescent properties, can be adapted.

When cerium is used alone, scintillator emission occurs at 410 nm and ambient temperature. However, when cerium and terbium are used simultaneously, the emission of the scintillator is in the range of 500 to 550 nm. In the latter case, the luminescence intensity is particularly high.

The amount of cerium added affects the rate of luminescence decay, which increases with cerium content and is always lower than the rate of decay obtained with the oxyorthosilicate of U.S. Pat. No. 4,647,781. expensive.

According to the invention, the scintillator properties are also improved by partially replacing the lanthanide Ln by another lanthanide Ln' having a higher atomic number. This allows the effective atomic number 2 of the material and its density d to be increased, while the absorption coefficients for X-rays and l or gamma rays are thus improved.

After all, the silicates used in the present invention have the advantage of an apatite-type structure, which remains the same and stable from ambient temperature up to the melting temperature of silicic acid, whereas cerium and Lanthanium oxyorthosilicates decompose before their melting point. Therefore, the segregation of cerium in the lanthanide silicates according to the invention is less than that observed in oxyorthosilicates. Therefore, the crystal properties (cry
Staline quality) and higher amounts of cerium can be used to increase the luminescence decay rate.

Other features and advantages of the invention can be deduced from a consideration of the following non-limiting examples and with reference to the drawings. The drawing schematically shows an X-ray and l or gamma-ray detection device according to the invention.

Example 1: Gd9.28Ceo, o5(SiO2)6o
A mixed oxide powder was first prepared from very pure Gd2O3, SiO2 and CeO2. 556.99 of Gd2o3 in an alumina crucible for this purpose.
g, 2.86 g of CeO2 and 119.g of SiO□.
36 g and then about 1500° in air
Calcined for 48 hours at C and then cooled to ambient temperature. The formula thus obtained is then: Gdg,2gCe
0o, os (8104)s 02 silicate powder was placed in an iridium crucible (diameter 60 mm, height 60 mm).
) and then heated to the melting point of the silicate powder, close to 1900°C, protected from atmospheric oxygen to form a molten bath.

A single mass of tetra-lanthanide silicate was then contacted with the molten bath. This nucleus was cut parallel to the a crystal direction of the hexagonal lattice of the compound. The nucleus was then slowly pulled up in a rotational motion relative to itself. This led to the gradual formation of single crystals at the ends of the core.

This resulted in a homogeneous single crystal with a length of 30 nm and a diameter of 70 mm. The single crystal was then subjected to an annealing treatment at 1200'C under a hydrogen atmosphere in order to reduce the tetravalent cerium ions possibly present in the crystal to trivalent cerium ions.

Only trivalent cerium ions are responsive to scintillation at about 410 nm.

The single crystal thus obtained has a luminescence decay rate of approximately 30 ns (nanoseconds), in contrast to US Pat. No. 4,647,78 with the same cerium content.
For the rare earth oxyorthosilicate of No. 1, the luminescence decay rate was about 60 ns.

Example 2 553.91 of Gd2O3 was prepared as in Example 1 above.
g, 5.72 g of CeO2 and 119.3 of 5tO2
A lanthanide silicate single crystal with the formula: % formula % was produced from 6 g. A powder was prepared under the same conditions as in Example 1 above and converted to single crystals using the same procedure. The crystal emits light at about 410 nm, and its luminescence decay rate is about 27 nm.
It was s.

Examples 3-5: Ln9.23Ceo, 1(SiO4)6
Single crystal of 02 [Ln represents La (Example 3), Yb (Example 4) and Lu (Example 5) J Below: 498.91 g of La2O3, 5.72 g of CeO2 and 119 of 5102 .62 g; or 645.45 g of Yb2o3, 6.11 g of CeO□
and 127.94 g of SiO2; or 65 g of Lu2O3
5.25 g, 6.14 g of CeO2 and SiO2
Example 2 above except that 128.63 g of
A lanthanide silicate powder was prepared using a similar operating procedure.

A single crystal was then produced as in Example 1 above and subjected to an annealing treatment as in Example 1 above. The single crystals obtained were all scintillators emitting at about 410 nm, and their luminescence decay rate was about 40 ns.

Example 6: Gd9.13CeO,05TbO,15(
SiO4) 602 single crystal first Gd2O3 547.
A similar operating procedure was used as in Example 1 above, except that there was present a mixture of powders consisting of 91 g of SiO2, 2.86 g of CeO2, 9.09 g of Tb2O3 and 119.36 g of SiO2. Next, a single crystal was produced from this powder according to the same operating procedure as in Example 1 above.

The single crystal was then subjected to an annealing treatment at a temperature of 1200° C. in a nitrogen atmosphere for 48 hours. As a result, a scintillator that emits light at a wavelength of 500 to 550 nm was obtained.

Examples 7 to 9 As in Example 6 above, Ln9.13 CeO,0
5Tbo, ts(SiO4)602 (wherein, Ln is La
, Yb or Lu) was produced. The obtained single crystals emitted light at a wavelength of 500-550 nm after annealing.

Example 10 Using the same operating procedure as in Example 1, Gd8.23
A single crystal of LuCeo, 1(8i04)602 was produced. First, 498.51g of Gd2o3, 6 of Lu2O3
6.49 g, 120.48 g of 5102, CeO
A lanthanide silicate powder was prepared as in Example 1 above starting from 5.75 g of □.

A single crystal was then produced from the powder according to the same operating procedure as in Example 1, and then annealed at 1200'C under a hydrogen atmosphere for 48 hours. The obtained single crystal was a scintillator that emitted light at a wavelength of about 410 nm. The luminescence decay rate of this scintillator was 35 ns.

Examples 11-13 Ln8.23Ln'Ce as in Example 9,
A single crystal of 1(SiO4)602 (wherein Ln and Ln' represent lanthanides shown in Table 1 below) was produced. These single crystals also emitted at a wavelength of approximately 410 nm. The decay rates of these single crystals are shown in Table 1 below.

Example 14 Gd8,1 according to the same operating procedure as in Example 1
A single crystal of 8LuCeo, o5Tbo, 1(SiO4) 60□ was produced. First, 495.49 g of Gd2O3
, 66.49 g of Lu2O3, 2.88 g of CeO2
, 9.17 g of Tb2O3 and 120.4 of 5tO2
A lanthanide silicate powder was prepared as in Example 1 above starting from 8 g.

A single crystal was then produced from the powder according to the same procedure as in Example 1, and then annealed at 1200° C. in a hydrogen atmosphere for 48 hours. The single crystal obtained was a scintillator that emitted light at wavelengths in the range of 500-550 nm.

The single crystals of lanthanide silicates according to the invention can be used as scintillators in X-ray and l- or gamma-ray detectors. Such a detector is shown schematically in the drawing.

It can be seen in the figure that the detector includes a scintillator 1 and a photoelectric detector 3 for detecting light from the scintillator. The scintillator-1 has an envelope (envelope).
5, for example made of aluminum and internally coated with a reflective material 7 such as barium sulfate. When scintillator 1 is irradiated with gamma rays that have passed through the aluminum envelope, light is generated by the scintillator. Although the emitted light is directed in all directions, it is reflected by the reflective material 7 and introduced into the photomultiplier tube 3.

An amplifier 9 amplifies the output of the photomultiplier tube 3.

The aforementioned detector can be used in particular for medical imaging by positron emission tomography. In this diagnostic method, positron emitter elements are substituted for natural isotopes in biological molecules injected into the patient.
ter element) is incorporated. The presence of these molecules or their metabolites is then detected in the body part by means of positron emission and the pair of lanthanide silicate single crystals according to the invention is used to detect annihilation photons, ie gamma rays.

The above-mentioned detector can also be used in drilling wells to detect X-rays and l or gamma rays emitted by different geological formations after a previous emission. The detector is capable of distinguishing between different geological formations.

An oil exploration device incorporating a scintillator is described, for example, in EP 231 693.

Table 1 ``ns,za Ln'ICeo,, (Sin4)60□
Example Ln Ln' Decaying speed n511
Gd Yb 3512
La Lu 4013 La
Yb 40 In the drawing, 1: scintillator 5 = envelope 92 amplifier 3: photomultiplier tube 7: reflective material

Claims (1)

[Claims] (1) The scintillator has the formula: (Ln_1_-_x__1_-_x__2_-_x___
3Ln'_x__1Ce_x__2Tb_x__3)_
9__. _3_3(SiO_4)_6O_2 (in the formula, Ln
and Ln' are different from each other and are La, Gd, Yb and Lu
x_1, x_2, and x_3 represent rare earth elements selected from 1. An X-ray and/or gamma-ray detector incorporating a scintillator characterized by being composed of a lanthanide silicate single crystal represented by the formula and a photoelectric detector for detecting light emitted from the scintillator. 2. Detector according to claim 1, characterized in that x_1 and x_3 are equal to zero. (3) The detector according to claim 2, wherein 0.005≦x_2≦0.02. (4) The detector according to claim 1, characterized in that x_1 is equal to zero. (5) The detector according to claim 4, wherein x_2 and x_3 are 0.003≦x_2≦0.01 0.005≦x_3≦0.002. (6) The detector according to claim 1, characterized in that x_3 is equal to zero. (7) x_1 and x_2 are 0.05≦x_1≦0.2 0.005≦x_2≦0.02 and 0.055≦x_
Claim 6 characterized in that 1+x_2≦0.22.
Detector as described. (8) The detector according to claim 1, wherein x_1, x_2 and x_3 are greater than zero. (9) The detector according to claim 8, wherein x_1, x_2, and x_3 are 0.05≦x_1≦0.2, 0.003≦x_2≦0.01, and 0.005≦x_3≦0.02. .